Soft vinyl chloride resins, ethylene/vinyl acetate resins, thermoplastic urethane resins, nylon 12, etc. have hitherto been used as materials which give hard rubbery or leather-like molded articles. They, however, have certain properties which still require improvements, for example, cold resistance in the soft vinyl chloride resins and nylon 12, abrasion resistance in the ethylene/vinyl acetate resins, and moldability in the thermoplastic urethane resins. These properties constitute a setback in exploiting their utility.
As described in Japanese Patent Publication No. 22468/1981, a polyamide-based elastomer having moderate rigidity and flexibility can be obtained by mixing a polyamide resin and an ionic ethylene copolymer. This polyamide-based elastomer has relatively improved cold resistance, particularly impact strength at low temperatures, in addition to thermal resistance and abrasion resistance which the polyamide resins inherently possess, but the improvements are still not sufficient. Moreover, it has poor rubbery elasticity because of its high rigidity.
On the other hand, as described in Japanese Patent Application (OPI) No. 125153/80, mixtures of polyamide resins and copolymers of ethylene and unsaturated carboxylic acids can be crosslinked by mixing under heat in the. presence of an organic peroxide. (The term "OPI" as used herein means an "unexamined published application".) However, their impact resistance is still insufficient though it is comparatively improved, and there is a fear of coloration.
Further, Japanese Patent Application (OPI) No. 240749/85 proposes an amine-crosslinkable rubber composition which contains a copolymer comprising from 53 to 86.6 mole % of an ethylene unit, from 13 to 45 mole % of an alkyl acrylate unit, and from 0.2 to 5 mole % of a maleic anhydride unit and a primary or secondary polyamine. There is no description, however, with respect to a composition containing a polyamide resin.
Also, according to the investigation of the present inventors, it was found that the above-described crosslinkable rubber composition is not only unable to provide molded articles having a rigidity adapted for use as various kinds of automobile parts, sport shoe soles, etc. whose flexural modulus (as defined in JIS K7203) is in the order of from 500 to 15,000 kg/cm.sup.2 but also is unsatisfactory from the viewpoint of the practical heat-resisting temperature.